How long to wait before brick acid?

[cdbe]

Unfortunately it's very messy so will need a good scrub - I did some last year after about a week and I'm sure it attacked the joints a bit. Also any advice on acid dilution - it's currently 36%.

 

[stuart45]

Soak the wall first, helps keep the acid reaction on the surface.
Neutralise later with an alkaline solution.
What have you built with? Engineering bricks?

 

[^woody^]

As long as possible and as weak as possible.

At least a month and perhaps start with 1:10. Wet the wall before and straight away afterwards.

 

[cdbe]

Thanks. It's recycled Accrington's. I did want to do it before I lifted my scaffold planks for the next lift but I suppose I can do it just as easily on the way down.

 

[stuart45]

Many years ago I worked on a job building with similar bricks to Accringtons. These type of bricks are really difficult to keep clean.
The method they used was to joint up, then a bit later rub the brickwork with small bits of carpet and then joint up again.
Although it sounds a bit stupid, it took off the thicker bits of mortar stuck to the bricks and left a thin smear over the wall.
Although it looked a mess it made the acid clean up much easier.

 

[opps]

Where I am working at the moment, the customer is having weather struck pointing on the existing flettons. I know the pointers, they are great. I asked them why there was so much cement smudge on the bricks. I had only ever seen them working on red rubbers. They explained that they would use a brushed on 25% dilute brick acid mix and then hose it off. At a guess, some of the smudges were up to 3 weeks old.

The bricks look fine now but they did clean the bricks with super evil acid and pressure washing before the pointing- not sure if that makes any difference or not.

 

[stuart45]

Surprised they are get Flettons smudged up, they are usually really easy to lay and repoint.